Summary of Lake releases for 2016 compared to 2013 and the last big El Nino event (1997-1998), SLR/IRL

Today I am sharing in full Dr Gary Goforth’s ( http://garygoforth.net/resume.htm) note and summary of Lake Okeechobee releases for 2016 compared to 2013 and the last big El Nino event (1997-1998) as presented to Martin County. Please click on slides for larger view and thank you Dr Goforth for helping us with the numbers.

….Slide 1

From the desk of Dr Gary Goforth regarding slide presentation:

1. More than 113,000 acre feet (36.9 billion gallons) of Lake water (“blackwater”) has been dumped to the River/Estuary during the first 20 days of the 2016 Lake releases; this is equal to 27% of the entire 147-day 2013 event, and 11% of the 1998 event.

2. The 2016 average daily rate of Lake releases is slightly less than the average 1998 rate, and more than twice the 2013 rate.

3. A distinguishing feature of the 2016 event is exceptionally high rates of C-44 Basin runoff in combination with the high Lake releases.

4. The 2016 average daily C-44 Basin runoff rate is 4 times the runoff rate of 1998, and more than twice the 2013 rate.

5. The 2016 average daily rate of combined flows through S-80 is more than the 1998 rate, and more than twice the 2013 rate.

6. The 2016 maximum daily rate of combined flows through S-80 is less than the 1998 maximum flow, but more than the 2013 maximum flow.

7. The 2016 Lake releases have already contributed more than twice the annual TMDL for phosphorus and nitrogen.

2016 data are preliminary and subject to revision.

I was on the IRL yesterday and travelled from the St. Lucie Inlet to the Ft. Pierce inlet – I saw no pockets of clear water and visibility was only 6 inches – 18 inches. I can’t imagine the sea grasses are getting any sunlight; I certainly didn’t see any sea grasses from the surface.

Gary

SLIDE PRESENTATION:

….Slide 1

Notes: 1. More than 113,000 acre feet (36.9 billion gallons) of Lake water (“blackwater”) has been dumped to the River/Estuary during the first 20 days of the 2016 Lake releases; this is equal to 27% of the entire 2013 releases, and 11% of the 1997-1998 event. 2. The 2016 average daily rate of Lake releases is slightly less than the average 1998 rate, and more than twice the 2013 rate. 3. The 2016 average daily C-44 Basin runoff rate is 4 times the runoff rate of 1998, and more than twice the 2013 rate. 4. The 2016 average daily rate of combined flows through S-80 is more than the 1998 rate, and more than twice the 2013 rate. 5. The 2016 maximum daily rate of combined flows through S-80 is less than the 1998 maximum flow, but more than the 2013 maximum flow. 6. The 2016 Lake releases have contributed more than twice the annual TMDL for phosphorus and nitrogen. 7. 2016 data are preliminary and subject to revision.

7 thoughts on “Summary of Lake releases for 2016 compared to 2013 and the last big El Nino event (1997-1998), SLR/IRL”

The fourfold increase in C-44 basin runoff was an issue that came up indirectly in one of Jacqui’s prior blogs because this is often referred to as “local” runoff or non-Lake O water. However, much of the water that flows into C-44 historically flowed into the lake and now bypasses the lake completely and is sent straight to C-44 as “C-44 basin runoff”. At the time, I was asking about the Levee L-65 canal and the water flowing out it via S-153 into C-44 (historical Lake O water). Does any of that water originate north of the Martin County Line? Apparently there is a plug in L-65 about 8 miles north of C-44. If I am looking at the numbers correctly, S-153 has dumped 25,000 acre feet into C-44 this year (from 1/1/2016 to 2/9/2016). From 1/1/2013 to 2/9/2013 that number was a much smaller 490 acre feet. Is that correct? If so, that as 50-fold increase over 2013! It looks like the whole land area within Martin County north of Kanner Highway and west of Warfiled Blvd is approx. 39,000 acres. Where is all that water coming from?

Your question of where the water came from is a good one. I don’t have a final answer for you; I had to do a little forensic hydrology, and I think I have a preliminary answer for you.

Short answer (preliminary): A combination of
1. landowners within the basin pumping water out of their canal system before, during and after the storm event, and
2. possibly some water from the FP&L power plant cooling pond.

I will follow up with staff of the Water Management District to see if they can help answer this question.

Long answer (preliminary):

First some background.
• The S-153 Basin covers approximately 12,600 acres (19.7 square miles) beginning along the north boundary of the FPL cooling reservoir and extending approximately 4 miles north across SR 710 up to Martin Highway (SR 714).
o The average ground elevation runs from about 25 ft near the Lake to about 50 ft in the north.
o The basin encompasses the Orlando Ridge that historically separated areas that flowed to the Lake from areas that flowed to Allapattah Slough (aka Allapattah Flats).
o Yes, there is an earthen plug in the L-64/L-65 borrow canals that separates the S-153 basin from the C-59 Basin (aka Taylor Creek Nubbin Slough basin) to the north. The plug is located about 8 miles north of the C-44 Canal (see attached maps).
o The land use is a mix of wetlands, forested wetlands, improved pasture, low density residential, remnant citrus and some row crops.

• By design, structure S-153 is to be operated to maintain water levels in the L-65 borrow canal between 18.6 and 19.1 ft. Between 1/1/2016 and 2/23/2016 it was operated such that water levels ranged from 18.6 – 19.2 ft.

• You are correct – between 1/1/2016 and 2/8/2016 approximately 25,000 acre feet was discharged through S-153 to the C-44 basin, the majority (about 16,000 acre feet) was discharged during the 5-day period from 1/28 – 2/1.
o This 5-day flow volume was the highest 5-day volume ever recorded in the 33-year period of record for the structure.
o The maximum flow was 1,826 cfs on January 29. The highest stormwater flow reported for the structure was 2,637 cfs on 9/25/1983.
o Attached is a chart of the annual flow discharged from the S-153 structure into C-44. Annual flows ranged from 2,500 acre feet to more than 340,000 acre feet.
o The 2016 flow for Jan-2/8 was about 50 times the 2013 flow for the same period.

• We can compare flows through S-153 to the rainfall that fell on the basin by converting the flow to “unit area runoff” – which is the flow divided by the area (“acre feet” divided by “acres” yields units of “feet”). For example, for the 40-day period 1/1 – 2/8, the flow through S-153 was about 25,000 acre feet. The unit area runoff for this period is (25,000 divided by the basin area of 12,600 acres = ) about 2 ft. During that same period, the rainfall measured at the nearby S-135 structure was 11.6 inches, or about 1.0 ft. Hence the unit area runoff was about twice the rainfall for that period.

• For the 5-day period, the area contributed about 1.3 ft of flow compared to receiving about 0.5 ft of rainfall.

• For the period 1986-2015, the annual unit area runoff ranged from less than 0.5 ft to more than 27 feet per year, with an average of 4.7 ft. This is more than 3 times the average of the C-44 Basin (which includes the S-153 basin) of 1.5 ft.

OK – back to your question: The basin discharged almost twice the volume of rain that fell directly on the basin, so where did the excess water come from?
• Perhaps landowner(s) within the basin was discharging water from their canal system in excess of rainfall. Often farmers will pump prior to, during and after a rain event – particularly if the crops are in a phase that is intolerant to getting their roots too wet. After the storm they will pump back into their canal system. So in the short-term there may be excess discharged – but in the long-term this will balance out with water drawn in for water supply. Hence this can’t explain the annual flows in excess of rainfall.

• Perhaps the excess water came from outside the basin?
o To the west of the S-153 Basin/L-65 borrow canal is the S-135 Basin, and the water level in this basin is held around 14 ft – so it would be impossible for water from the S-135 Basin to “seep” uphill to the L-65 Borrow Canal which is held around 18.8 ft.
o To the east of the S-153 Basin is the 6,600-acre cooling pond/reservoir of the FPL power plant.
 There was a dike failure on or about 10/31/1979 which resulted in a flow of 3,900 cfs through S-153. Steps were taken to strengthen the dike and as far as I know there has not been any more problems.
 As a very rough estimate of the water surface, I checked Google Earth – which suggests the water surface in the FPL reservoir was around 33 ft at the time of the last survey. Since 33 ft is considerably higher than the water level in the L-65 canal (18.8 ft), there exists an approximate 14-ft hydraulic gradient (“head”) that represents the potential for seepage from the FPL reservoir to the L-65 canal.
 Technically this reservoir is outside the S-153 Basin, although there are multiple structures from the FPL property that cross under the railroad tracks and into the L-65 canal, e.g., a set of culvert from the 450-ac Barley Barber Swamp. I know nothing about these although I suspect they are not used often for conveying water. I found no flow records in the Water Management District’s database.
 At this time, I can only surmise that flow from the FP&L property accounts for the annual discharges from S-153 that were in excess of basin rainfall.

• Preliminary answer:
o The potential may exist for landowners within the basin to pump more water off their land than fell from rainfall (short-term phenomenon).
o The potential exists for seepage and surface water from the FP&L property to flow into the L-65 borrow canal and subsequently to be discharged at S-153. (short and long-term phenomenon).

I will follow up with staff of the Water Management District to see if they can help answer this question.
Others questions:
Does any of that water originate north of the Martin County Line? No
From 1/1/2013 to 2/9/2013 that number was a much smaller 490 acre feet. Is that correct? Yes

I like to pull up the flow numbers from Google Earth and was looking at the FPL reservoir wondering if it might be a source. It looks like they draw water out of C-44 to fill the reservoir? So is it just going in a circle?

A few weeks ago Jacqui asked me if I knew what S-80âs max was and I got sidetracked reading the SFWD reports on that 1979 dike failure. If I remember correctly, I thought it was interesting that the reports didnât really say that the reservoir was overfilled, as I have heard people say, but one theory is that there was erosion piping to the old railroad borrow pits that were dug in the 1920s in that area before the FPL plant was built. I have the old 1940 aerials overlaid in Google Earth and can show exactly where those pits were â not far from the inside edge of the dike. They also investigated but dismissed vandalism that occurred at S-153 that dramatically lowered L-65 right before the failure and could have caused a pressure gradient through the dike. Apparently one way to make a dike less susceptible to failure is to not draw the water âheadâ so low on the back side?

I know you know the story, but the numbers are unreal when the dike let loose. 100,000 cfs into L-65 and directly into C-44 and the sugarcane fields, S-308 flowed backwards into Lake O, S-80 maxed out at 15,800 cfs â so my answer for Jacqui was twice the flow that we are at now if the conditions are right but that peak was only a few hours. I guess the design max is 16,900 cfs â instant death for the St. Lucie.

Yes, FP&L pulls water out of the C-44 to replace water lost to seepage and net evaporation (i.e., rainfall minus evaporation). As I understand, there are also multiple pumps around the reservoir that collect seepage and return it to the reservoir. I donât think there are any routine discharges from the reservoir to the L-65 canal. My first inquiry to District staff was a dead end â they couldnât explain the very high discharges at S-153 observed in 1986, 1987, 1998, 1999 and 2004-2008. I need to contact different staff and will keep you apprised.

Correct, the District found 2 âprobableâ causes:

1. Piping to the north end of the old railroad borrow pits

2. Deep piping in the foundation below the embankment, leading to a blow out at the toe of the levee

FP&L found 2 additional âpossibleâ causes

1. Piping of the foundation to the L-65 canal

2. Piping of the shallow foundation emerging at the downstream toe

Correct â minimizing the hydraulic gradient is a good thing!

The flow values and magnitude of impact were amazing â and to think that it occurred just before midnight and throughout the night folks were mobilized to respond (and evacuate) â in total darkness … The poor River/Estuary to get hammered following Hurricane David in September of that year.